If CS6 is patched to 8.0.2 and the .idml you receive won't open it most likely means it isn't really .idml, but just a .indd with the extension changed. Make sure your colleagues know how to creat .idml files for you.

Nothing to do with your problem, but I really wonder why you have 952 identical links on your background. I cannot see the actual design since they are missing, but I am quite sure it could have done with a single file on each page.

You're welcome. BTW, I agree with the others here that you should rework that background to be one image per page. 300+ tiny individual links for a background is just bound to cause trouble; even more so since they are reduced to almost 25%, and disproportionately, at that.